versión impresa ISSN 1726-4634

Resumen

In order to ascertain the range of activity of DDT in preventing Carrion's disease (verruga peruana) and cutaneous leishmaniasis (uta) in the native population of endemic zones, two controled field experiments were carried out with the insecticide. One was in Surco and the other in San Juan, both localities in the Rimac Valley. In Surco, a locality with indigenous population, DDT was applied in 1947 and 1948 to the "pircas" (stone walls) within the town as well as in the adjacent fields but not in human dwellings. In San Juan, DDT was applied only to the walls of the buildings in 1947 and 1948, and to the neighboring "pircas" in 1949. San Juan is the city of an agricultural school, in which the majority of the student population is not inmune to either Carrion's disease or cutancous leishmaniasis. To evaluate the results of these experiments, the decrease in the "verruga" and "uta" incidence and the reduction in the population of the insect vector, Phlebotomus verrucarum, were taken as parameters. A summary of the results so far obtained is as follows: 1. Surco experiment. a) Two years after the onset of the experiment, the incidence of cutaneous leishmaniasis in dogs decreased from 22.0 to 1.6 per cent. b) The incidence of both "verruga" as well as "uta" in the pre - school children evaluated six years after the first spraying of insecticide decreased so greatly that it suggests that transmission had stopped altogether during that lapse of time. The few cases observed during the experiment probably were infected outside the experimental zone. c) In spite of the fact that DDT was applied only to the "pircas", the sand fly (P. verrucarum) population decreased in all the dwellings which served as sample experimental areas up to and including 1953. d) In three caves also used as sample experimental areas in which Phlebotomus noguchii was present the sandfly population also decreased appreciably, but only between 1948 and 1950. It is assumed that the sandfly population decrease was caused by the disapperence of roedent hosts from the caves rather that to a direct action of the insecticide that was sprayed on the neighboring "pircas". 2. San Juan Experiment. a) The spraying of DDT in 1947 considerably reduced the incidence of verruga during the remaining of that school year (June to December) among the student population while during 1948 not a single case of the disease was reported. b) Although no more blood cultures were made after May, 1949, new cases of verruga were extremely rare among students up. to 1953. c) In all buildings sprayed with insecticide the sandfly population decreased to insignificant levels, except with small variations which persisted to the end of 1953. d) As a result of spraying insecticide in the student's dormitories a remarkable reduction of sandfly population was observed on the neighboring "pircas", even though the "pircas" were not sprayed with DDT during 1947 and 1948.